Machines that have the capability of automatically substituting different types of tools in order to perform various machining or measuring operations on a workpiece are quite widespread and well-known in the art. Modular tools are simply releasably secured to the machine, which allows dispensing with the use of specific machines for each specific operation.
Whenever such tools contain an electric circuit, power supply need to be provided to the circuit, or at least some form of releasable electrical connection between the tool support needs to be foreseen.
Modular probe heads are often mounted on a standard tool-holder, for example a Morse tapered shank, which is then releasably connected to a spindle or a rotary axis machine tool, to carry out all sorts of measurements and dimensional controls. This is often done before a working operation such as milling, boring or any other machining operation is carried out on a workpiece. Such modular probe heads are meant e.g. to ensure the proper positioning of the workpiece, or to check that its dimensions lie within an acceptable range, before starting the machining operation.
The power supply for such probe heads is often problematic, insofar as the shanks to which the probes' housings are attached usually do not contain any electrical energy source or electrical connections. When the probe is connected to a rotary axis, as it is almost invariably the case, it is then impossible to connect any electrical wire to the probe, which must be fully autonomous insofar as power supply is concerned.
Built in batteries are regularly used for supplying energy to the probe head in order to perform the measuring operations, and possibly also for transmitting information to a machine control unit. The limited lifetime of the batteries requires though their regular recharging and/or manual replacement, which is fastidious and time-consuming.
As an alternative to batteries, various systems have been proposed to solve this electric power supply problem, in converting mechanical energy into electrical energy thanks to generators.
U.S. Pat. No. 5,564,872 describes a wireless probe using a built-in hydraulic turbine fed by compressed air of fluids as an electromechanical converter. Similarly U.S. Pat. No. 4,716,657 and US2007006473 disclose a measuring probe provided with a turbine supplied by a pressurised fluid for generating electric power.
Those solutions require hermetic ducts to carry the fluid flow, and also a precise sealing of the tool support with the probe when mounting it in order to avoid fluid leakage or pressure loss. This is not easily realized and involves a particular design of the tool-holder. In most cases the connection of the probe to the fluid circuit (e.g. a cutting fluid line) must be performed manually and separately, when it is possible at all.
Another solution for the power generation is disclosed by JP3223602, where the spindle of the machine tool drives directly an electric generator in the probe in rotation, while the housing of the probe is fixed to a non-rotating element of the machine tool's head. This requires a second mechanical connection in addition to the standard tapered shank, and thus prevents from a quick and easy change of the tools when passing from one machine operation to another.
There is hence a need for an autonomous electric power generation system for modular probe heads containing an electric circuit, free of all the limitations above.